Nicotinamide adenine dinucleotide is transported into mammalian mitochondria

Abstract

Mitochondrial NAD levels influence fuel selection, circadian rhythms, and cell survival under stress. It has alternately been argued that NAD in mammalian mitochondria arises from import of cytosolic nicotinamide (NAM), nicotinamide mononucleotide (NMN), or NAD itself. We provide evidence that murine and human mitochondria take up intact NAD. Isolated mitochondria preparations cannot make NAD from NAM, and while NAD is synthesized from NMN, it does not localize to the mitochondrial matrix or effectively support oxidative phosphorylation. Treating cells with nicotinamide riboside that is isotopically labeled on the nicotinamide and ribose moieties results in the appearance of doubly labeled NAD within mitochondria. Analogous experiments with doubly labeled nicotinic acid riboside (labeling cytosolic NAD without labeling NMN) demonstrate that NAD(H) is the imported species. Our results challenge the long-held view that the mitochondrial inner membrane is impermeable to pyridine nucleotides and suggest the existence of an unrecognized mammalian NAD (or NADH) transporter.

Subcellular NAMPT‐mediated NAD+ salvage pathways and their roles in bioenergetics and neuronal protection after ischemic injury

“…Mitochondrial occurrence of NMNAT3 in mammalian cells is also controversial (Zhang et al 2003;Berger et al 2005;Felici et al 2013). The current model for mitochondrial NAD + biosynthesis is that NAM is converted to NMN and NMN is then transported into mitochondria for subsequent NAD + synthesis by NMNAT3 (Formentini et al 2009;Nikiforov et al 2011;Stein and Imai 2012;Davila et al 2018) (Fig. 3c).…”

The Aging Metabolome—Biomarkers to Hub Metabolites

“…The two pools can interact via the malate aspartate shuttle, and possibly via the direct transporter of NAD into the mammalian mitochondria. [ 85 ] The age‐dependent dysregulation in NAD + metabolism [ 37,38 ] and the well‐characterized mitochondrial loss associated with aging [ 86,87 ] are consistent with the loss of mitochondrial TCA function. Based on this observation there is significant interest in supplementation of NAD + precursors (e.g., nicotinamide mononucleotide (NMN)) to compensate for aging‐related metabolic dysfunction in NAD metabolism.…”

Differential processing and localization of human Nocturnin controls metabolism of mRNA and nicotinamide dinucleotide metabolites

“…NAD cofactors exhibit high flux between redox states through crucial roles in many pathways, including both biosynthetic and catabolic pathways, cellular bioenergetics, protection from and generation of reactive oxygen species, and signal transduction (summarized in Figure 8b) (52)(53)(54). NAD cofactors also interchange between cytoplasmic and mitochondrial compartments, either indirectly through shuttle pathways or -as indicated by recent evidence -directly (53,(55)(56)(57)(58). Most relevant to NOCT, NAD is also interconverted between phosphorylation states, mediated by specific cytoplasmic and mitochondrial NAD kinases, NADK1 and NADK2, respectively (Figure 8b) (59,60).…”